Phytoplankton community distribution in relation to environmental parameters in three aquaculture systems in a Chinese subtropical eutrophic bay

There is concern about the impact of expanding coastal aquaculture activity, particularly in China, with the biggest aquaculture industry in the world. We conducted 3 cruises to the oyster, kelp and fish farms of the Xiangshan Bay during the winter-spring transition (02/2009), winter (01/2010) and spring (04/2010). Our aim was to explore the spatial heterogeneity of the phytoplankton community in different culture habitats and evaluate the effects of mariculture on phytoplankton. Different culture types formed unique small-scale habitats that exhibited various environmental gradients and forms of phytoplankton community patchiness. Both environmental (i.e. temperature, salinity, transparency, suspended solids, dissolved oxygen, pH, dissolved inorganic nitrogen, PO4-P, SiO3-Si, NIP, and total organic carbon) and phytoplankton (i.e. cell density, chlorophyll a, species richness, main dominant species, and community structure) parameters were significantly different among the 3 culture habitats. Canonical correspondence analysis showed that phytoplankton distribution was mainly influenced by temperature, nutrition, salinity and suspended solids. Oyster and kelp farming effectively alleviated coastal eutrophication and also increased species richness and diversity; fish farming did not. Temperature elevation caused by the thermal discharge from a power plant induced phytoplankton blooms during the winter and winter-spring transition. Nevertheless, the filtering effect of suspended oysters dramatically reduced microalgal biomass. The kelp and oyster farms were much better than the fish farm in terms of water quality, phytoplankton composition, and habitat restoration function. These results provide guidelines for future policy-making in aquaculture as well as eutrophication control and management.